Centerless honing machines are in general use for honing external cylindrical surfaces on a series of workpieces, such as pins, shafts and many other types of workpieces. In many cases, the workpieces have previously been machined by a centerless grinding machine or a variety of other machine tools. The honing machine gives the cylindrical surfaces a much smoother finish, while also improving the roundness of the cylindrical surfaces and bringing the size of the cylindrical surfaces into closer agreement with the desired size, the agreement being very close with very small tolerances, in most cases.
A conventional honing machine generally comprises a pair of closely spaced special rollers which are continually rotated by a suitable drive. The rollers support the successive workpieces and cause them to rotate, while also causing the workpieces to travel axially along the length of the rollers. Generally, a continuous stream of workpieces is supplied to the rollers at one end. The workpieces are honed as they travel along the length of the rollers, and the finished workpieces are removed as a continuous stream from the rollers at the opposite end.
The workpieces are honed by pressing honing elements, such as honing stones, against the traveling workpieces as they are rotated by the rollers. Thus, the workpieces are honed by the abrasive action of the stones. Generally, the honing stones are oscillated rapidly in a direction parallel with the axes of the workpieces, so as to produce a better finish.
Generally, the honing stones are mounted on supporting members which are guided for movement in a direction perpendicular to the axes of the workpieces.
The honing stones are pressed against the workpieces by pressing devices acting upon the supporting members. Such pressing devices may take the form of springs, fluid pressure operated cylinders, or other fluid pressure operated devices. Either air pressure or hydraulic pressure may be employed, although air pressure is generally preferred.
The honing stones remove a small amount of stock from the workpieces by abrasive action, so that the size of the cylindrical surfaces, after honing, is slightly smaller than before honing. It is generally desired to hold the finished size of the honed workpieces to very close tolerences. Thus, it is important to have the honing machine remove enough stock from the workpieces, but not too much.
The amount of stock removed from the workpieces is a function of the pressure which is exerted between the honing stones and the workpieces. Increasing the pressure increases the amount of stock removed, and vice versa.
To provide for close control over the finished size of the honed workpieces, conventional honing machines may have manually operable means for regulating the force applied to the stone supporting members. When the force is developed by fluid pressure cylinders or other fluid pressure actuated devices, a manually adjustable pressure regulating may be employed to vary the fluid pressure supplied to the fluid pressure cylinder. This method of manual control requires that the operating person who operates the machine be highly skilled. Moreover, the operator must give close attention to the adjustment of the honing machine on a virtually continuous or highly frequent basis, to maintain the desired close tolerences. Thus, the operation of a conventional centerless honing machine involves a high labor cost.